Network Working Group                                      K. McCloghrie
Request for Comments: 1213                      Hughes LAN Systems, Inc.
Obsoletes: RFC 1158                                              M. Rose
                                       Performance Systems International
                                                                 Editors
                                                              March 1991


           Management Information Base for Network Management
                       of TCP/IP-based internets:
                                 MIB-II

Status of this Memo

   This memo defines the second version of the Management Information
   Base (MIB-II) for use with network management protocols in TCP/IP-
   based internets.  This RFC specifies an IAB standards track protocol
   for the Internet community, and requests discussion and suggestions
   for improvements.  Please refer to the current edition of the "IAB
   Official Protocol Standards" for the standardization state and status
   of this protocol.  Distribution of this memo is unlimited.

Table of Contents

   1. Abstract...............................................    2
   2. Introduction ..........................................    2
   3. Changes from RFC 1156 .................................    3
   3.1 Deprecated Objects ...................................    3
   3.2 Display Strings ......................................    4
   3.3 Physical Addresses ...................................    4
   3.4 The System Group .....................................    5
   3.5 The Interfaces Group .................................    5
   3.6 The Address Translation Group ........................    6
   3.7 The IP Group .........................................    6
   3.8 The ICMP Group .......................................    7
   3.9 The TCP Group ........................................    7
   3.10 The UDP Group .......................................    7
   3.11 The EGP Group .......................................    7
   3.12 The Transmission Group ..............................    8
   3.13 The SNMP Group ......................................    8
   3.14 Changes from RFC 1158 ................. .............    9
   4. Objects ...............................................   10
   4.1 Format of Definitions ................................   10
   5. Overview ..............................................   10
   6. Definitions ...........................................   12
   6.1 Textual Conventions ..................................   12
   6.2 Groups in MIB-II .....................................   13
   6.3 The System Group .....................................   13

   6.4 The Interfaces Group .................................   16
   6.5 The Address Translation Group ........................   23
   6.6 The IP Group .........................................   26
   6.7 The ICMP Group .......................................   41
   6.8 The TCP Group ........................................   46
   6.9 The UDP Group ........................................   52
   6.10 The EGP Group .......................................   54
   6.11 The Transmission Group ..............................   60
   6.12 The SNMP Group ......................................   60
   7. Acknowledgements ......................................   67
   8. References ............................................   69
   9. Security Considerations ...............................   70
   10. Authors' Addresses ...................................   70

1.  Abstract

   This memo defines the second version of the Management Information
   Base (MIB-II) for use with network management protocols in TCP/IP-
   based internets.  In particular, together with its companion memos
   which describe the structure of management information (RFC 1155)
   along with the network management protocol (RFC 1157) for TCP/IP-
   based internets, these documents provide a simple, workable
   architecture and system for managing TCP/IP-based internets and in
   particular the Internet community.

2.  Introduction

   As reported in RFC 1052, IAB Recommendations for the Development of
   Internet Network Management Standards [1], a two-prong strategy for
   network management of TCP/IP-based internets was undertaken.  In the
   short-term, the Simple Network Management Protocol (SNMP) was to be
   used to manage nodes in the Internet community.  In the long-term,
   the use of the OSI network management framework was to be examined.
   Two documents were produced to define the management information: RFC
   1065, which defined the Structure of Management Information (SMI)
   [2], and RFC 1066, which defined the Management Information Base
   (MIB) [3].  Both of these documents were designed so as to be
   compatible with both the SNMP and the OSI network management
   framework.

   This strategy was quite successful in the short-term: Internet-based
   network management technology was fielded, by both the research and
   commercial communities, within a few months.  As a result of this,
   portions of the Internet community became network manageable in a
   timely fashion.

   As reported in RFC 1109, Report of the Second Ad Hoc Network
   Management Review Group [4], the requirements of the SNMP and the OSI

   network management frameworks were more different than anticipated.
   As such, the requirement for compatibility between the SMI/MIB and
   both frameworks was suspended.  This action permitted the operational
   network management framework, the SNMP, to respond to new operational
   needs in the Internet community by producing this document.

   As such, the current network management framework for TCP/IP- based
   internets consists of: Structure and Identification of Management
   Information for TCP/IP-based internets, RFC 1155 [12], which
   describes how managed objects contained in the MIB are defined;
   Management Information Base for Network Management of TCP/IP-based
   internets: MIB-II, this memo, which describes the managed objects
   contained in the MIB (and supercedes RFC 1156 [13]); and, the Simple
   Network Management Protocol, RFC 1098 [5], which defines the protocol
   used to manage these objects.

3.  Changes from RFC 1156

   Features of this MIB include:

   (1)  incremental additions to reflect new operational
        requirements;

   (2)  upwards compatibility with the SMI/MIB and the SNMP;

   (3)  improved support for multi-protocol entities; and,

   (4)  textual clean-up of the MIB to improve clarity and
        readability.

   The objects defined in MIB-II have the OBJECT IDENTIFIER prefix:

      mib-2      OBJECT IDENTIFIER ::= { mgmt 1 }

   which is identical to the prefix used in MIB-I.

3.1.  Deprecated Objects

   In order to better prepare implementors for future changes in the
   MIB, a new term "deprecated" may be used when describing an object.
   A deprecated object in the MIB is one which must be supported, but
   one which will most likely be removed from the next version of the
   MIB (e.g., MIB-III).

   MIB-II marks one object as being deprecated:

      atTable

   As a result of deprecating the atTable object, the entire Address
   Translation group is deprecated.

   Note that no functionality is lost with the deprecation of these
   objects: new objects providing equivalent or superior functionality
   are defined in MIB-II.

3.2.  Display Strings

   In the past, there have been misinterpretations of the MIB as to when
   a string of octets should contain printable characters, meant to be
   displayed to a human.  As a textual convention in the MIB, the
   datatype

      DisplayString ::=
          OCTET STRING

   is introduced.  A DisplayString is restricted to the NVT ASCII
   character set, as defined in pages 10-11 of [6].

   The following objects are now defined in terms of DisplayString:

      sysDescr
      ifDescr

   It should be noted that this change has no effect on either the
   syntax nor semantics of these objects.  The use of the DisplayString
   notation is merely an artifact of the explanatory method used in
   MIB-II and future MIBs.

   Further it should be noted that any object defined in terms of OCTET
   STRING may contain arbitrary binary data, in which each octet may
   take any value from 0 to 255 (decimal).

3.3.  Physical Addresses

   As a further, textual convention in the MIB, the datatype

      PhysAddress ::=
          OCTET STRING

   is introduced to represent media- or physical-level addresses.

   The following objects are now defined in terms of PhysAddress:

      ifPhysAddress
      atPhysAddress
      ipNetToMediaPhysAddress

   It should be noted that this change has no effect on either the
   syntax nor semantics of these objects.  The use of the PhysAddress
   notation is merely an artifact of the explanatory method used in
   MIB-II and future MIBs.

3.4.  The System Group

   Four new objects are added to this group:

      sysContact
      sysName
      sysLocation
      sysServices

   These provide contact, administrative, location, and service
   information regarding the managed node.

3.5.  The Interfaces Group

   The definition of the ifNumber object was incorrect, as it required
   all interfaces to support IP.  (For example, devices without IP, such
   as MAC-layer bridges, could not be managed if this definition was
   strictly followed.)  The description of the ifNumber object is
   changed accordingly.

   The ifTable object was mistaken marked as read-write, it has been
   (correctly) re-designated as not-accessible.  In addition, several
   new values have been added to the ifType column in the ifTable
   object:

      ppp(23)
      softwareLoopback(24)
      eon(25)
      ethernet-3Mbit(26)
      nsip(27)
      slip(28)
      ultra(29)
      ds3(30)
      sip(31)
      frame-relay(32)

   Finally, a new column has been added to the ifTable object:

      ifSpecific

   which provides information about information specific to the media
   being used to realize the interface.

3.6.  The Address Translation Group

   In MIB-I this group contained a table which permitted mappings from
   network addresses (e.g., IP addresses) to physical addresses (e.g.,
   MAC addresses).  Experience has shown that efficient implementations
   of this table make two assumptions: a single network protocol
   environment, and mappings occur only from network address to physical
   address.

   The need to support multi-protocol nodes (e.g., those with both the
   IP and CLNP active), and the need to support the inverse mapping
   (e.g., for ES-IS), have invalidated both of these assumptions.  As
   such, the atTable object is declared deprecated.

   In order to meet both the multi-protocol and inverse mapping
   requirements, MIB-II and its successors will allocate up to two
   address translation tables inside each network protocol group.  That
   is, the IP group will contain one address translation table, for
   going from IP addresses to physical addresses.  Similarly, when a
   document defining MIB objects for the CLNP is produced (e.g., [7]),
   it will contain two tables, for mappings in both directions, as this
   is required for full functionality.

   It should be noted that the choice of two tables (one for each
   direction of mapping) provides for ease of implementation in many
   cases, and does not introduce undue burden on implementations which
   realize the address translation abstraction through a single internal
   table.

3.7.  The IP Group

   The access attribute of the variable ipForwarding has been changed
   from read-only to read-write.

   In addition, there is a new column to the ipAddrTable object,

      ipAdEntReasmMaxSize

   which keeps track of the largest IP datagram that can be re-assembled
   on a particular interface.

   The descriptor of the ipRoutingTable object has been changed to
   ipRouteTable for consistency with the other IP routing objects.
   There are also three new columns in the ipRouteTable object,

      ipRouteMask
      ipRouteMetric5
      ipRouteInfo

   the first is used for IP routing subsystems that support arbitrary
   subnet masks, and the latter two are IP routing protocol-specific.

   Two new objects are added to the IP group:

      ipNetToMediaTable
      ipRoutingDiscards

   the first is the address translation table for the IP group
   (providing identical functionality to the now deprecated atTable in
   the address translation group), and the latter provides information
   when routes are lost due to a lack of buffer space.

3.8.  The ICMP Group

   There are no changes to this group.

3.9.  The TCP Group

   Two new variables are added:

      tcpInErrs
      tcpOutRsts

   which keep track of the number of incoming TCP segments in error and
   the number of resets generated by a TCP.

3.10.  The UDP Group

   A new table:

      udpTable

   is added.

3.11.  The EGP Group

   Experience has indicated a need for additional objects that are
   useful in EGP monitoring.  In addition to making several additions to
   the egpNeighborTable object, i.e.,

      egpNeighAs
      egpNeighInMsgs
      egpNeighInErrs
      egpNeighOutMsgs
      egpNeighOutErrs
      egpNeighInErrMsgs
      egpNeighOutErrMsgs

      egpNeighStateUps
      egpNeighStateDowns
      egpNeighIntervalHello
      egpNeighIntervalPoll
      egpNeighMode
      egpNeighEventTrigger

   a new variable is added:

      egpAs

   which gives the autonomous system associated with this EGP entity.

3.12.  The Transmission Group

   MIB-I was lacking in that it did not distinguish between different
   types of transmission media.  A new group, the Transmission group, is
   allocated for this purpose:

      transmission OBJECT IDENTIFIER ::= { mib-2 10 }

   When Internet-standard definitions for managing transmission media
   are defined, the transmission group is used to provide a prefix for
   the names of those objects.

   Typically, such definitions reside in the experimental portion of the
   MIB until they are "proven", then as a part of the Internet
   standardization process, the definitions are accordingly elevated and
   a new object identifier, under the transmission group is defined.  By
   convention, the name assigned is:

      type OBJECT IDENTIFIER ::= { transmission number }

   where "type" is the symbolic value used for the media in the ifType
   column of the ifTable object, and "number" is the actual integer
   value corresponding to the symbol.

3.13.  The SNMP Group

   The application-oriented working groups of the IETF have been tasked
   to be receptive towards defining MIB variables specific to their
   respective applications.

   For the SNMP, it is useful to have statistical information.  A new
   group, the SNMP group, is allocated for this purpose:

      snmp   OBJECT IDENTIFIER ::= { mib-2 11 }

3.14.  Changes from RFC 1158

   Features of this MIB include:

   (1)  The managed objects in this document have been defined
        using the conventions defined in the Internet-standard
        SMI, as amended by the extensions specified in [14].  It
        must be emphasized that definitions made using these
        extensions are semantically identically to those in RFC
        1158.

   (2)  The PhysAddress textual convention has been introduced to
        represent media addresses.

   (3)  The ACCESS clause of sysLocation is now read-write.

   (4)  The definition of sysServices has been clarified.

   (5)  New ifType values (29-32) have been defined.  In
        addition, the textual-descriptor for the DS1 and E1
        interface types has been corrected.

   (6)  The definition of ipForwarding has been clarified.

   (7)  The definition of ipRouteType has been clarified.

   (8)  The ipRouteMetric5 and ipRouteInfo objects have been
        defined.

   (9)  The ACCESS clause of tcpConnState is now read-write, to
        support deletion of the TCB associated with a TCP
        connection.  The definition of this object has been
        clarified to explain this usage.

   (10) The definition of egpNeighEventTrigger has been
        clarified.

   (11) The definition of several of the variables in the new
        snmp group have been clarified.  In addition, the
        snmpInBadTypes and snmpOutReadOnlys objects are no longer
        present.  (However, the object identifiers associated
        with those objects are reserved to prevent future use.)

   (12) The definition of snmpInReadOnlys has been clarified.

   (13) The textual descriptor of the snmpEnableAuthTraps has
        been changed to snmpEnableAuthenTraps, and the definition
        has been clarified.

   (14) The ipRoutingDiscards object was added.

   (15) The optional use of an implementation-dependent, small
        positive integer was disallowed when identifying
        instances of the IP address and routing tables.

4.  Objects

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using the subset of Abstract Syntax Notation One (ASN.1) [8]
   defined in the SMI.  In particular, each object has a name, a syntax,
   and an encoding.  The name is an object identifier, an
   administratively assigned name, which specifies an object type.  The
   object type together with an object instance serves to uniquely
   identify a specific instantiation of the object.  For human
   convenience, we often use a textual string, termed the OBJECT
   DESCRIPTOR, to also refer to the object type.

   The syntax of an object type defines the abstract data structure
   corresponding to that object type.  The ASN.1 language is used for
   this purpose.  However, the SMI [12] purposely restricts the ASN.1
   constructs which may be used.  These restrictions are explicitly made
   for simplicity.

   The encoding of an object type is simply how that object type is
   represented using the object type's syntax.  Implicitly tied to the
   notion of an object type's syntax and encoding is how the object type
   is represented when being transmitted on the network.

   The SMI specifies the use of the basic encoding rules of ASN.1 [9],
   subject to the additional requirements imposed by the SNMP.

4.1.  Format of Definitions

   Section 6 contains contains the specification of all object types
   contained in this MIB module.  The object types are defined using the
   conventions defined in the SMI, as amended by the extensions
   specified in [14].

5.  Overview

   Consistent with the IAB directive to produce simple, workable systems
   in the short-term, the list of managed objects defined here, has been
   derived by taking only those elements which are considered essential.

   This approach of taking only the essential objects is NOT
   restrictive, since the SMI defined in the companion memo provides

   three extensibility mechanisms: one, the addition of new standard
   objects through the definitions of new versions of the MIB; two, the
   addition of widely-available but non-standard objects through the
   experimental subtree; and three, the addition of private objects
   through the enterprises subtree.  Such additional objects can not
   only be used for vendor-specific elements, but also for
   experimentation as required to further the knowledge of which other
   objects are essential.

   The design of MIB-II is heavily influenced by the first extensibility
   mechanism.  Several new variables have been added based on
   operational experience and need.  Based on this, the criteria for
   including an object in MIB-II are remarkably similar to the MIB-I
   criteria:

   (1)  An object needed to be essential for either fault or
        configuration management.

   (2)  Only weak control objects were permitted (by weak, it is
        meant that tampering with them can do only limited
        damage).  This criterion reflects the fact that the
        current management protocols are not sufficiently secure
        to do more powerful control operations.

   (3)  Evidence of current use and utility was required.

   (4)  In MIB-I, an attempt was made to limit the number of
        objects to about 100 to make it easier for vendors to
        fully instrument their software.  In MIB-II, this limit
        was raised given the wide technological base now
        implementing MIB-I.

   (5)  To avoid redundant variables, it was required that no
        object be included that can be derived from others in the
        MIB.

   (6)  Implementation specific objects (e.g., for BSD UNIX) were
        excluded.

   (7)  It was agreed to avoid heavily instrumenting critical
        sections of code.  The general guideline was one counter
        per critical section per layer.

   MIB-II, like its predecessor, the Internet-standard MIB, contains
   only essential elements.  There is no need to allow individual
   objects to be optional.  Rather, the objects are arranged into the
   following groups:

      - System
      - Interfaces
      - Address Translation (deprecated)
      - IP
      - ICMP
      - TCP
      - UDP
      - EGP
      - Transmission
      - SNMP

   These groups are the basic unit of conformance: This method is as
   follows: if the semantics of a group is applicable to an
   implementation, then it must implement all objects in that group.
   For example, an implementation must implement the EGP group if and
   only if it implements the EGP.

   There are two reasons for defining these groups: to provide a means
   of assigning object identifiers; and, to provide a method for
   implementations of managed agents to know which objects they must
   implement.